Power management

ABSTRACT

According to an embodiment of the invention the timing of one or more local communication windows can be defined using equations such that one or more local communication windows for two or more devices overlap. For example the periods between two consecutive local communication windows can be defined using a periodic equation such as: LAP Cycle Period=Δ*2 n . In this equation n=0, 1, 2, . . . , N, where N and Δ can be fixed. For example, N and Δ can be numbers that are predetermined for a given network, a given set of network devices, etc. In one embodiment every device can become active every Δ*2 n  superframes. The frequency (n) can be determined based on, for example, incoming or outgoing message traffic, power consumption needs, etc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from the following U.S. ProvisionalPatent Applications with the following Ser. Nos. 60/765,980 filed Feb.6, 2006; 60/775,518 filed Feb. 21, 2006; 60/825,110 filed Sep. 8, 2006;and 60/828,743 filed Oct. 9, 2006; each of which are hereby incorporatedherein by reference in the respective entirety of each.

TECHNICAL FIELD

The present invention relates to communications, and more particularly,some embodiments relate to power save modes in a communication system.

DESCRIPTION OF THE RELATED ART

With the many continued advancements in communications technology, moreand more devices are being introduced in both the consumer andcommercial sectors with advanced communications capabilities.Additionally, advances in processing power and low-power consumptiontechnologies, as well as advances in data coding techniques have led tothe proliferation of wired and wireless communications capabilities on amore widespread basis.

For example, communication networks, both wired and wireless, are nowcommonplace in many home and office environments. Such networks allowvarious heretofore independent devices to share data and otherinformation to enhance productivity or simply to improve theirconvenience to the user. One such communication network that is gainingwidespread popularity is an exemplary implementation of a wirelessnetwork such as that specified by the WiMedia-MBOA (Multiband OFDMAlliance). Other exemplary networks include the Bluetooth®communications network and various IEEE standards-based networks such as802.11 and 802.16 communications networks, to name a few.

With the proliferation of portable and low-power consumption devices,techniques for extending battery life or otherwise reducing powerconsumption have been developed. Consequently, an important goal in thedesign of wireless networks is to enable long operation time for batterypowered devices. An effective method to extend battery life is to enabledevices to turn off completely (i.e., hibernate) for long periods oftime, where a long period is relative to the superframe duration.

For example, one way to utilize the hibernation power saving mechanismas outlined by the WiMedia MAC protocol is to provide two powermanagement modes in which a device can operate: the active mode and thehibernation mode. Devices in the active mode transmit and receivebeacons in every superframe. Devices in the hibernation mode hibernatefor multiple superframes and do not transmit or receive in thosesuperframes, thus saving energy. These periods are typically fixedperiodic active and hibernation periods.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

According to various embodiments of the invention a device can announcebroadcast traffic in the global access period. Thus, a destination canchange its local access period every global access period. By announcinga local access period during a global access period it can be morelikely that a source device in a network will receive the informationbecause all devices should be active during the global access period. Bychecking during a receiver device's known local access period a sourcedevice can reduce the amount of time that it spends in the idle statewaiting for its destination to become active because, for example, thesource can wake from hibernation at the same time that the destinationawakens from hibernation. A device can awaken for its local accessperiod and during the local access period a source device can schedule atransmission and transmit information to the device.

According to another embodiment of the invention the timing of one ormore local access periods can be defined using equations such that oneor more local access periods for two or more devices overlap. Forexample the periods between two consecutive local access periods can bedefined using a periodic equation such as: LAP Cycle Period=Δ*2^(n). Inthis equation n=0, 1, 2, . . . , N, where N and Δ can be fixed. Forexample, N and Δ can be numbers that are predetermined for a givennetwork, a given set of network devices, etc. In one embodiment everydevice can become active every Δ*2^(n) superframes. The frequency (n)can be determined based on, for example, incoming or outgoing messagetraffic, power consumption needs, etc.

According to another embodiment of the invention, a system and method toprovide alignment of hibernation and active cycles is provided. When onedevice receives a beacon from one of its neighbors it can be implementedto check for the neighboring device's global cycle start countdown valueand to compare it's global cycle start countdown value with its own. Ifthe beacon from the neighboring device contains a value that isdifferent from the device's own global cycle start countdown, the devicecan be implemented to check a predefined condition.

For example, if a device's global cycle start time falls into the firsthalf of a neighbor's global cycle, then the device changes its ownglobal cycle start time to the global cycle start time of that neighbor.Otherwise, the device does nothing. Note, however, that in oneembodiment both devices can be configured to check this condition fromtheir own perspectives. In one embodiment the condition used is checkedby both devices D1 and D2 but the condition is designed such that itwill become true for one or the other of the two devices, to help ensurethat there won't be any instability in the this protocol, for almost allcases. In one embodiment a “tie-breaker” can be included for cases whereboth devices will be led to the same conclusion.

According to another embodiment of the invention, a system and method toprovide alignment of hibernation and active cycles is provided formultiple (e.g., more than 2) devices that are in range of each other.For example, if a device's global cycle start time falls into the first256/K superframes of a neighbor's global cycle, then the device changesits own global cycle start time to the global cycle start time of thatneighbor. Otherwise, the device does nothing. In one embodiment, K canbe the number of different global active cycle start times observed bythe device. In one embodiment a “tie-breaker” can be included for caseswhere two or more devices will be led to the same conclusion.

Other features and aspects of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresin accordance with embodiments of the invention. The summary is notintended to limit the scope of the invention, which is defined solely bythe claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments of the invention. Thesedrawings are provided to facilitate the reader's understanding of theinvention and shall not be considered limiting of the breadth, scope, orapplicability of the invention. It should be noted that for clarity andease of illustration these drawings are not necessarily made to scale.

FIG. 1 is a block diagram illustrating one possible configuration of awireless network that can serve as an example environment in which thepresent invention can be implemented.

FIG. 2 is a diagram illustrating bandwidth that can be divided intosuperframes, which in turn can be divided into time slots.

FIG. 3 is a diagram illustrating one example of the power savingmechanism in accordance with one embodiment of the invention.

FIG. 4 is a flowchart illustrating one example method in accordance withthe systems and methods described herein.

FIG. 5 is a flowchart illustrating one example method in accordance withthe systems and methods described herein.

FIG. 6 is a block diagram illustrating example of global and localaccess periods.

FIG. 7 is a block diagram illustrating another example of global andlocal access periods.

FIG. 8 is a block diagram illustrating another example of global andlocal access periods.

FIG. 9 is a block diagram illustrating an example of one devicecommunicating with multiple devices.

FIG. 10 is a block diagram illustrating an example of overlapping globalaccess periods.

FIG. 11 is a flowchart illustrating an example method for setting aglobal access period.

FIG. 12 is a flowchart illustrating an example method for alignment ofhibernation and active cycles in accordance with the systems and methodsdescribed herein.

FIG. 13 is a flowchart illustrating another example method for alignmentof hibernation and active cycles in accordance with the systems andmethods described herein.

FIG. 14 is a flowchart illustrating additional details of one of thesteps of FIG. 13.

FIG. 15 is a flowchart illustrating additional details of one of thesteps of FIG. 13.

The figures are not intended to be exhaustive or to limit the inventionto the precise form disclosed. It should be understood that theinvention can be practiced with modification and alteration, and thatthe invention be limited only by the claims and the equivalents thereof.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

With the many continued advancements in communications technology, moreand more devices are being introduced in both the consumer andcommercial sectors with advanced communications capabilities.Additionally, advances in processing power and low-power consumptiontechnologies, as well as advances in data coding techniques have led tothe proliferation of wired and wireless communications capabilities on amore widespread basis.

For example, communication networks and other channels, both wired andwireless, are now commonplace in many home and office environments. Suchnetworks allow various heretofore independent devices to share data andother information to enhance productivity or simply to improve theirconvenience to the user. One such communication network that is gainingwidespread popularity is an exemplary implementation of a wirelessnetwork such as that specified by the WiMedia-MBOA (Multiband OFDMAlliance). Other exemplary networks include the Bluetooth®communications network and various IEEE standards-based networks such as802.11 and 802.16 communications networks, to name a few.

With the proliferation of portable and low-power consumption devices,techniques for extending battery life, otherwise reducing powerconsumption, or managing power usage have been developed. Consequently,one goal in the design of wireless networks can be to enable longoperation time for battery powered devices. An effective method toextend battery life is to enable devices to turn off some or all oftheir functions (i.e., hibernate) for relatively long periods of time.For example, a long period might be long relative to a superframeduration.

In one embodiment, the present invention provides systems and methodsfor power management in electronic devices. A power saving mechanism canenable battery-powered and other power-conscious devices, such as WiNetdevices for example, to utilize hibernation modes for powerconservation. In another embodiment, hibernation modes offered by theWiMedia MAC protocol are utilized for the power management, allowingdevices to dynamically change the durations of hibernation and activemodes via WiNet negotiation. As would be apparent to one of ordinaryskill in the art after reading this description this mechanism can beimplemented in alternative environments.

For example, one way to utilize the hibernation power saving mechanismas outlined by the WiMedia MAC protocol is to provide two powermanagement modes in which a device can operate: the active mode and thehibernation mode. In this environment, devices in the active modetransmit and receive beacons in every superframe; while devices in thehibernation mode hibernate for multiple superframes and do not transmitor receive in those superframes, thus saving energy. These periods mighttypically be fixed periodic active and hibernation periods.

Various networks and other communication protocols allow their devicesto go into hibernation and active modes. In one embodiment, theinvention enables the devices to synchronize their active cycles toenable devices to have their awake times better aligned temporally. Assuch, in one embodiment, they can awaken, conduct their respectiveactivities, and return to hibernation mode without have to wait aninordinate amount of time for the other devices with which they arecommunicating to awaken.

For example, in one environment, the WiMedia WiNet specification definesa mechanism that enables devices to periodically go into active mode anddynamically adjust their hibernation duty cycles. In order tosynchronize with neighbors' local cycles, a device might typicallymaintain a global cycle start time for its neighbors. One embodiment ofthe invention allows a system and method for enabling devices to aligntheir global cycle start times.

Before describing the invention in detail, it is useful to describe anexample environment in which the invention can be implemented. One suchexample is a wireless beaconing network in which multiple electronicdevices (for example, computers and computing devices, cellulartelephones, personal digital assistants, motion and still cameras, amongothers) can communicate and share data, content and other informationwith one another. One example of such a network is that specified by theWiMedia standard (within WiMedia and Multi-Band OFDM Alliance). Fromtime-to-time, the present invention is described herein in terms of adistributed network or in terms of a WiMedia standard. Description interms of these environments is provided to allow the various featuresand embodiments of the invention to be portrayed in the context of anexemplary application. After reading this description, it will becomeapparent to one of ordinary skill in the art how the invention can beimplemented in different and alternative environments. Indeed,applicability of the invention is not limited to a distributed wirelessnetwork, nor is it limited to a WiMedia standard described as oneimplementation of the example environment.

Most network standards specify policies or rules that govern thebehavior of network connected devices. The WiMedia standard specifiesthe mechanism and policies that are to be followed by W-USB and WiNetcompliant devices in order to allow for an ad hoc and distributednetwork of such devices to operate efficiently.

In most distributed networks, the network of the devices is maintainedby requiring all devices to announce parameters such as their presence,their capabilities and their intentions for reserving transmission slotsand so on. For example, with the WiMedia standard, this can be doneduring what are referred to as beacon period time slots. According tothis standard, devices joining the network are expected to monitor thebeacon period to learn about the network status and parameters beforeattempting to use the network. In other network configurations, beaconperiods are similarly used to allow management of network devices asdescribed more fully below. Thus, beacon periods are one form of windowor network period during which scheduling or other housekeepingactivities can be conducted. Beacon periods in the above-referencedstandard, and other time periods used for scheduling or otherhousekeeping chores in other network configurations, are generallyreferred to as scheduling windows.

Devices are typically allowed to enter a power save mode to conservepower and possibly prolong operation. For example, battery operateddevices may enter a sleep mode or even a deep-sleep mode, wherein one ormore of their functions are diminished or shut down in order to conservepower. Depending on the environment, devices may be allowed to enterinto a sleep mode for short or long periods of time. For example, asleep mode can be an energy-saving mode of operation in which some orall components are shut down or their operation limited. Manybattery-operated devices, such as notebook computers, cell phones, andother portable electronic devices support one or more levels of a sleepmode. For example, when a notebook computer goes into one level of sleepmode, it may turn off the hard drive and still allow the user to performoperations, only powering up the hard drive when access is needed. In adeeper level of sleep, the computer may further turn off the display. Inyet a further level of sleep, the computer may enter a hibernate state.Likewise, other electronic devices communicating across a communicationchannel may have similar sleep states and may power down unnecessary orunused components, including an RF transceiver, depending on a number offactors such as elapsed time, activities and so on. As described below,in accordance with one embodiment, devices may be prompted to enter asleep mode upon completion of scheduling or other housekeepingactivities and be configured to awaken for scheduled activities such as,for example, communication activities.

In one embodiment sleep mode can be, for example, an energy-saving modeof operation for a portion of a superframe in which some or allcomponents are shut down or their operation limited but during whichbeacons are sent. (Some or all of the components can power up when abeacon is to be sent.) In another embodiment hibernate can be, forexample, an energy-saving mode of operation for multiple superframes inwhich some or all components are shut down or their operation limitedand during which beacons are not sent.

FIG. 1 is a block diagram illustrating one possible configuration of awireless network that can serve as an example environment in which thepresent invention can be implemented. Referring now to FIG. 1, awireless network 120 is provided to allow a plurality of electronicdevices to communicate with one another without the need for wires orcables between the devices. A wireless network 120 can vary in coveragearea depending on a number of factors or parameters including, forexample, the transmit power levels and receive sensitivities of thevarious electronic devices associated with the network. Examples ofwireless networks can include the various IEEE and other standards asdescribed above, as well as other wireless network implementations.

With many applications, the wireless network 120 operates in arelatively confined area, such as, for example, a home or an office. Theexample illustrated in FIG. 1 is an example of an implementation such asthat which may be found in a home or small office environment. Of coursewireless communication networks and communication networks in generalare found in many environments outside the home and office as well. Inthe example illustrated in FIG. 1, wireless network 120 includes acommunication device to allow it to communicate with external networks.More particularly, in the illustrated example, wireless network 120includes a modem 140 to provide connectivity to an external network suchas the Internet 146, and a wireless access point 142 that can provideexternal connectivity to another network 144.

Also illustrated in the example wireless network 120 are portableelectronic devices such as a cellular telephone 110 and a personaldigital assistant (“PDA”) 112. Like the other electronic devicesillustrated in FIG. 1, cellular telephone 110 and PDA 112 cancommunicate with wireless network 120 via the appropriate wirelessinterface. Additionally, these devices may be configured to furthercommunicate with an external network. For example, cellular telephone110 is typically configured to communicate with a wide area wirelessnetwork by way of a base station.

Additionally, the example environment illustrated in FIG. 1 alsoincludes examples of home entertainment devices connected to wirelessnetwork 120. In the illustrated example, electronic devices such as agaming console 152, a video player 154, a digital camera/camcorder 156,and a high definition television 158 are illustrated as beinginterconnected via wireless network 120. For example, a digital cameraor camcorder 156 can be utilized by a user to capture one or more stillpicture or motion video images. The captured images can be stored in alocal memory or storage device associated with digital camera orcamcorder 156 and ultimately communicated to another electronic devicevia wireless network 120. For example, the user may wish to provide adigital video stream to a high definition television set 158 associatedwith wireless network 120. As another example, the user may wish toupload one or more images from digital camera 156 to his or her personalcomputer 160 or to the Internet 146. This can be accomplished bywireless network 120. Of course, wireless network 120 can be utilized toprovide data, content, and other information sharing on a peer-to-peeror other basis, as the provided examples serve to illustrate.

Also illustrated is a personal computer 160 or other computing deviceconnected to wireless network 120 via a wireless air interface. Asdepicted in the illustrated example, personal computer 160 can alsoprovide connectivity to an external network such as the Internet 146.

In the illustrated example, wireless network 120 is implemented so as toprovide wireless connectivity to the various electronic devicesassociated therewith. Wireless network 120 allows these devices to sharedata, content, and other information with one another across wirelessnetwork 120. Typically, in such an environment, the electronic deviceswould have the appropriate transmitter, receiver, or transceiver toallow communication via the air interface with other devices associatedwith wireless network 120. These electronic devices may conform to oneor more appropriate wireless standards and, in fact, multiple standardsmay be in play within a given neighborhood. Electronic devicesassociated with the network typically also have control logic configuredto manage communications across the network and to manage theoperational functionality of the electronic device. Such control logiccan be implemented using hardware, software, or a combination thereof.For example, one or more processors, ASICs, PLAs, and other logicdevices or components can be included with the device to implement thedesired features and functionality. Additionally, memory or other dataand information storage capacity can be included to facilitate operationof the device and communication across the network.

Electronic devices operating as a part of wireless network 120 aresometimes referred to herein as network devices, members or memberdevices of the network or devices associated with the network. In oneembodiment devices that communicate with a given network may be membersor merely in communication with the network.

Some communication networks are divided into periods or frames that canbe used for communication and other activities. For example, asdiscussed above, some networks have a scheduling window such as, forexample, a beacon period, for scheduling upcoming communicationactivities. Also, some networks have a communication window during whichsuch communication activities take place. In the WiMedia-MBOA standard,the bandwidth is divided into superframes, which in turn are dividedinto time slots for the transmission and reception of data by thevarious electronic devices associated with the network.

An example of such time slots are illustrated in FIG. 2. Referring nowto FIG. 2, in this exemplary environment, the communication bandwidth isdivided into superframes 204 (two illustrated), each superframe 204itself being divided into a plurality of timeslots referred to as MediaAccess Slots 208. In the example environment, there are 256 media accessslots 208 in each superframe 204, although other allocations arepossible. Additionally, at the beginning of each superframe 204 is abeacon period 212, which is comprised of a plurality of beaconing slots.In some networks, the beacon period 212 is a period during which devicesreserve timeslots and exchange other housekeeping or status information.For example, in the WiMedia-MBOA distributed wireless network, thesuperframes comprise a beacon period 212, during which devices are awakeand receive beacons from other devices. Superframes in theabove-referenced standard, and other time periods used forcommunications among devices in other network configurations, with orwithout scheduling windows, are generally referred to herein ascommunication windows. As noted above, for clarity of description thepresent invention is described in terms of the example environment, andthus is at times described using the terms superframe and beacon period.As would be apparent to one of ordinary skill in the art after readingthis description, the invention applies to other communication formats,including the more general case utilizing scheduling windows andcommunication windows. Additionally, the invention is not limited toapplications where the bandwidth is divided into frames or windows, butcan be generally applied to communication channels and networks ofvarious protocols and configurations.

Having thus described an example environment in which the invention canbe implemented, various features and embodiments of the invention arenow described in further detail. Description may be provided in terms ofthis example environment for ease of discussion and understanding only.After reading the description herein, it will become apparent to one ofordinary skill in the art that the present invention can be implementedin any of a number of different communication environments (includingwired or wireless communication environments, and distributed ornon-distributed networks) operating with any of a number of differentelectronic devices and according to various similar or alternativeprotocols or specifications.

From time-to-time, the present invention is described herein in terms ofthese example environments. Description in terms of these environmentsis provided to allow the various features and embodiments of theinvention to be portrayed in the context of an exemplary application.After reading this description, it will become apparent to one ofordinary skill in the art how the invention can be implemented indifferent and alternative environments, and how the invention can beimplemented for non-hazardous as well as hazardous materials.

One embodiment of the invention provides a mechanism that enablesbattery-powered or other power sensitive communication devices toutilize the hibernation power saving mechanism offered by existingprotocols such as, for example, the WiMedia MAC protocol. In thisexample implementation, the invention can be implemented to provide anew dimension of traffic indication (for example, at the WiNETsub-layer), by enabling devices to go into hibernation mode unless theyhave traffic to transmit or they are “woken up” by their neighbors. Thiscan allow devices to dynamically change the durations of hibernation andactive modes via WiNET negotiation.

For energy efficiency, any or all of the following features can beimplemented in accordance with various embodiments of the invention. Inaccordance with one feature, in circumstances where there is no databuffered for transmission for a network device, that device is permittedto hibernate preferably for as long as possible or practical and is thuspreferably active for as short a time period as possible or practical.

In accordance with another feature that might be implemented, wherethere is data buffered for transmission for a network device, thatreceiving device can be permitted to remain active for as long as neededto receive the data. Preferably, that receiving device remains activeonly as long as needed to receive the data.

In accordance with yet another feature that might be implemented, tohelp prevent the target from hibernating for too long, a mechanism canbe provided for the traffic source to provide information to the targetregarding the next time that the source may have traffic for thattarget. This expected time can, for example, be based on trafficstatistical models, known requirements or other methods used at thesource device.

Inherently, in many situations, fixed duty cycles might not perform wellin all situations. Because the active and hibernation periods affectthroughput and energy consumption, fixed duty cycles for these periodsmay not always provide optimum performance. If the active period ischosen to be too small, there may not be enough time available to sendor receive traffic, potentially degrading throughput. If the activeperiod is too long, the device has less time to hibernate, potentiallyincreasing the energy consumption. Also, if the hibernation period istoo long, then the source device may need to wait a long period of timebefore the target is active, potentially causing throughput degradationand buffer overflows. Thus, fixed periods might not always lead tooptimal power conservation.

In the example environment, the Traffic Indication Map (“TIM”)Information Element (“IE”) provides a mechanism to indicate that anactive device has data buffered for transmission via PrioritizedContention Access (“PCA”) for one or more of its neighbors. Thismechanism allows a device that is not expecting traffic during a certainsuperframe to go into a power save mode, such as a sleep state, thussaving the device's energy. Because TIM IE is used to indicate trafficwithin the superframe, it can be considered as an intra-superframetraffic indication mechanism.

In accordance with one embodiment of the invention, a new dimension oftraffic indication can be provided. In terms of the example environment,for instance, at the WiNET sub-layer level an inter-superframe trafficindication mechanism can be provided. This mechanism in one embodimentis orthogonal to the TIM IE mechanism, and can improve devices' energysavings. In one implementation, a network device is permitted orinstructed to go into the hibernation mode whenever it does not havetraffic to transmit. The device, however, can be configured so as to notremain in hibernation mode for longer than a given period so that it canreceive traffic information from other network devices that may wish tocommunicate with it. Upon receiving this traffic information, thenetwork device will be able to determine whether to remain awake or whento next reawaken to receive the intended data.

In terms of the example environment, in one embodiment the device canremain asleep for a variable period of X superframes, and awaken inorder to receive traffic information from other network devices that maywish to communicate with it (for example, “WiNET traffic indications”from its WiNET neighboring devices in the example environment). Theindication, which can be referred to as a WiNET Traffic Indication(“WTI”) (although other designations are possible), can, in oneembodiment, be encoded in the source's beacon. For example theindication can be encoded in the WiNET Application Specific InformationElement (“ASIE”). Similar to the TIM IE, it can be implemented tocontain the DevAddr or other identification of every neighboring devicefor which WiNET traffic is buffered. Additionally, the trafficindication (for example, the WTI) can be used to indicate a recommendedhibernation period for each one of those neighbors.

In one embodiment, a first network device that wishes to communicatewith one of its hibernating neighbors can wait until that neighbor goesinto an active mode. In one embodiment, the maximum time period before adevice goes into an active mode can be designated as a predeterminedmaximum latency of X superframes. When the neighbor goes into the activemode, that neighbor's identification (for example, its DevAddr or otheridentifier) and the recommend hibernation period can be included in thefirst device's traffic indication. Note that in the example environmentthe MAC specification mandates that the hibernating devices advertisethe hibernation period (i.e., X), so the source device may know when thetarget will be active.

A device that receives a traffic indication that contains itsidentification (e.g., DevAddr) can be configured to remain in the activemode for as long as traffic indications included in received beaconscontain its identification. The traffic indicator thus acts as a “wakeup” message for a network device. This allows the device to remainasleep as long as it does not need to transmit information, and toawaken only periodically to check for traffic indications affecting it.Thus, the invention can be implemented in one embodiment so that thedefault behavior is hibernation unless wake up calls are received. Thiscan increase the hibernation period, thus potentially improving networkdevices' energy consumption.

In one embodiment as mentioned above, the sending device can include arecommended hibernation period. This recommended hibernation period canprovide information to the target device regarding how long the deviceshould hibernate before waking up again to receive traffic from thesource device sending this recommendation. Various methodologies can beused to determine this parameter, and may be implementation specific.Preferably, the parameter takes into account the expected trafficpatterns at the source device.

For example, in one embodiment, when a source device may have trafficfor multiple target devices the source device can send a recommendedhibernation period for each target device. Thus, for this example,assume that a source device S1 has traffic or plans to have traffic fortarget devices T1, T2, and T3. S1 can suggest that T2 and T3 bothhibernate during the time period when it plans to transmit traffic toT1. Similarly, S1 can suggest that T1 and T3 both hibernate during thetime period when it plans to transmit traffic to T2. Further, S1 cansuggest that T1 and T2 both hibernate during the time period when itplans to transmit traffic to T3. T1, T2, and T3 may or may nothibernate, however. For example, if T1 has additional traffic fromanother source it might not hibernate while S1 is communicating with T2,T3, or both, depending on when it receives or expects to receive thisadditional traffic, how much additional traffic T1 has, etc.

Whether the target device follows this recommend hibernation period maydepend on a number of factors such as its power capabilities, QoS(“Quality of Service”) constraints, network requirements, otherscheduled communications activities, etc. In one embodiment, whether itfollows the recommendation or not, the invention can be implemented suchthat the source device will hear the hibernation period (part of MACrules), and wait until the target is up again to send the data. Thesource can then keep the target active by including the target addressin the traffic indicator so long as there is traffic for that target.

Thus, according to the various embodiments described above, one featurethat can be provided is that in scenarios where no data is buffered fortransmission to a network device, that device will not receive a trafficindicator that contains its identification, and is able to hibernate. Ofcourse, if that device has other activities to perform or otherrequirements, it may awaken for other reasons. On the other hand, wherethere is data buffered for transmission to a target network device, orit is otherwise known that the target is designated to receive traffic,the target device receives a traffic indicator that contains itsidentification.

The target device can also receive a recommended hibernation period orother indication of when the communication is desired or scheduled. Assuch, the target device can transition to (or remain in) the active modeto receive this traffic at the proposed or desired time. Thus, a dynamicwake up period can be provided allowing the hibernation and wake uptimes to be tailored to ongoing or anticipated network activities for agiven device.

FIG. 3 is a diagram illustrating one example of the proposed mechanism.For the purposes of this example, it can be assumed that some IP trafficis buffered for transmission at the WiNET source. If the source is awareof when the target will wake up (for example, via MAC rules or otherprotocol), the source might wait until the target is designated to beawake before sending the traffic indicator (for example, the WTI). Wherethe source has no other designated activities, the source can alsoremain in the hibernation mode, and wake up only right before the targetwakes up (or otherwise be awake for some overlapping period.)

The source device goes into the active mode and transmits its trafficindicator identifying the target device. In one embodiment, the sourcedevice can wait until it detects the target beacon, indicating thetarget is active. Once the target is active, the source includes thetarget identification (e.g., the DevAddr) in its traffic indicator(e.g., WTI) encoded in the beacon. In one embodiment, the source devicekeeps including the target indicator in the beacon as long as there isdata buffered for the target. When no more data is buffered at thesource node for that target, the source device can recommend that thetarget hibernate.

Referring now to FIG. 4 a flowchart further illustrating the example ofFIG. 3 is discussed. In a step 400 a source is awake. The source can,for example, wake up right before it expects the target to wake up.Alternatively, the source can wake up at some time while the target isalready awake. Additionally, the source may already be awake, forexample, the source may have had traffic for other targets.

In one embodiment, the source device can wait until it detects thetarget beacon, step 402 indicating the target is active. Once the targetis active, in a step 404 the source device can go into the active modeand transmits its traffic indicator identifying the target device in astep 406. In another embodiment the source device can go into the activemode and transmits its traffic indicator identifying the target devicewithout waiting until it detects the target beacon. For example, thetransmission can be based on timing alone, thus, the source devicemight, in some embodiments, know when the target is going to be activeaccurately enough so that it does not need to wait for the target'sbeacon. Thus, step 402 may or may not be required in some embodiments.As discussed above, the transmissions from the source can includes thetarget identification (e.g., the DevAddr) in its traffic indicator(e.g., WTI) encoded in the beacon. In one embodiment, the source devicecan keep including the target indicator in the beacon as long as thereis data buffered for the target.

When no more data is buffered at the source node for that target, thesource device can recommend that the target hibernate in a step 408. Inone embodiment, the source device can recommend that the targethibernate for X communication windows (e.g., superframes 204). Thetarget may take that recommendation as an indication of when the nextburst of data from source may come in. Of course, the target may havereceived other recommendations from other sources it communicates withor may otherwise have network requirements. Therefore, the target mightnot follow the recommended hibernation duration, but can use it indetermining the best hibernation duration to meet its own requirementsor the expected traffic requirements of all its sources. Thus, dependingon other activities, both the source and the target can now hibernateand wake up later to exchange data. Just before hibernation, both ofthem announce their hibernation period based on MAC rules. Thus, theSource will be able to determine the Target's planned hibernationperiod, regardless of the recommendations made.

Various systems and methods of power management are described herein.These systems and methods generally use various communication windows totransmit and receive various information to and from each other. Some ofthese communication windows can be individual or local communicationwindows. A local access period can, in one embodiment, be an individualor local communication window. The local access period generallyreferences a time period or duration of time when an individual devicewakes for the purpose of sending or receiving transmissions from otherdevices. In some cases other devices can be awake during some or all ofthe individual devices local access period, for example, when one ormore of these other devices has traffic for the individual device.

A global communication window generally references a time period orduration of time when all devices, a plurality of devices, a referenceddevice, or a relevant set of devices is or should be in the active orwakeup mode to exchange information, for example, on a global level. Aglobal access period is a global communication window.

According to various embodiments of the invention a device can announcebroadcast traffic in a global access period. By announcing a localaccess period during a global access period it can be more likely that asource device in a network will receive the information because many, ifnot all of the devices in a neighborhood should be active during theglobal access period. A device can awaken for its local access periodand during the local access period a source device can schedule atransmission and transmit information to the device. In this way, powercan be managed by, in certain circumstances, allowing a source device tohibernate until a target device, also sometimes referred to as areceiver device or a recipient device wakes, rather than requiring thedevice to stay awake while waiting for the target device to wake up.

According to an embodiment, the timing of one or more local accessperiods can be defined using equations such that one or more localaccess periods for two or more devices overlap. For example the periodsbetween two consecutive local access periods can be defined using aperiodic equation. In this way power can be managed by, in oneembodiments, allowing a source device to calculate when a target devicewill wake. This can allow a source device to hibernate until a targetdevice wakes up, for example.

According to another embodiment of the invention, a system and method toprovide alignment of hibernation and active cycles is provided. When onedevice receives a beacon from one of its neighbors it can be implementedto check for the neighboring device's global cycle start countdown valueand to compare it's global cycle start countdown value with its own. Ifthe beacon from the neighboring device contains a global cycle startcountdown value that is different from the device's own global cyclestart countdown, the device can be implemented to check a predefinedcondition. For example, if a device's global cycle start time falls intothe first half of a neighbor's global cycle, then the device changes itsown global cycle start time to the global cycle start time of thatneighbor. Otherwise, the device does nothing.

According to another embodiment of the invention, a system and method toprovide alignment of hibernation and active cycles is provided formultiple devices that are in range of each other. When one devicereceives beacons from other neighbor devices it can be implemented tocheck for the neighboring devices' global cycle start countdown valuesand to compare these global cycle start countdown values with its own.For example, if a device's global cycle start time falls into the first256/K superframes of a neighbor's global cycle, then the device changesits own global cycle start time to the global cycle start time of thatneighbor. Otherwise, the device does nothing. In one embodiment, K canbe the number of different global active cycle start times observed bythe device. In one embodiment a “tie-breaker” can be included for caseswhere two or more devices will be led to the same conclusion.

In some of the examples of the systems and methods described herein onedevice waking up at the same time or just before one or more otherdevices is discussed. It will be understood, however, that generally,the systems and methods described herein can be applied to any situationin which some overlap exists between one device being awake and one ormore other devices being awake.

One example of a global access period, in terms of the exampleenvironment, can be the period of time during which a device is activeand able to exchange WiNet broadcast or multicast control traffic suchas, for example, Address Resolution Protocol (“ARP”) packets. The phraselocal access period of a device generally refers to the duration of timewhen or the time period during which the device is in the active modeand is ready to exchange local information. For example, in terms of theexample environment, the period of time during which a device is activeand able to exchange WiNet unicast packets (such as, for example, IPpackets).

In one embodiment, a global access period Information Element (“GAP IE”)is implemented, an example of which is shown in Table 1.

TABLE 1 GAP field format Bits: b15–b1 b0 GAP Countdown GAP Status

In this example, a global access period Status is set to “1” during theglobal access period. The GAP Countdown can be dynamically set toindicate the start of the next global access period. For example, theGAP Countdown can indicate the number of superframes until the start ofthe next global access period as illustrated in FIG. 7.

In one embodiment, the devices can be implemented such that the WiNetbridge (or other designated device) announces a GAP IE in its beacon. Ifa device is registered with a WiNet bridge, then that device can beconfigured such that it is active during the global access periodannounced by GAP IE of that bridge. The device can also include thereceived GAP IE in its beacon with a GAP Countdown decremented by 1.

If a device is not registered with a bridge, and it receives a beaconthat contains a GAP IE, that device can be configured so as to be activeduring the global access period announced by the received GAP IE. Thedevice can also include the received GAP IE in its beacon with a GAPCountdown decremented by 1. If the device receives two or more beaconswith different GAP IEs, the device can be configured to be active duringthe global access periods announced. For example, in one embodiment thedevice is active during the unions of global access periods announced inthe received GAP IEs. Because the device is active during all globalaccess periods, the device can announce any of the received GAP IEs withadjusted Countdown field as above.

If a device is not registered with a bridge, did not receive any GAP IE,and its beacon slot number is the smallest in all Beacon periodoccupancy Information Element (“BPOIE”) transmitted or received by thatdevice, then that device can create a new GAP IE and include it in itsbeacon. The device that creates the GAP IE is called the owner ofannounced global access period.

Preferably, devices should transmit their broadcast and multicastcontrol traffic as early as possible in the global access period. In oneembodiment, the owner of the global access period can decide on theglobal access period duration by simply timing out on not receivingcontrol traffic. Thus, in one embodiment, if no broadcast or multicastcontrol traffic is received or transmitted during a predetermined periodthe owner may terminate the global access period. For example, thepredetermined period can be some number of superframes. In oneembodiment when no broadcast or multicast control traffic is received ortransmitted during the last mGAPtimeout superframes, where mGAPtimeoutis some predetermined number of superframes, the owner may terminate theglobal access period. In one embodiment, however, the global accessperiod duration is not less than some predetermined minimum or longerthan some predetermined maximum. For example, in one embodiment, theglobal access period duration is not less mMinGAP or longer thanmMaxGAP. mMinGAP and mMaxGA can be predetermined numbers.

It will be understood, however, that in another embodiment, the owner ofthe global access period can decide on the global access period durationby simply timing out on not receiving control traffic after some periodof time that is not predetermined. Thus, the timing out can be based onno broadcast or multicast control traffic being received or transmittedand other factors. Thus, in one embodiment the time is not apredetermined period.

The GAP Countdown can be used to dictate the frequency of global accessperiod. The bridge or device that creates the GAP IE can use historicaldata of broadcast and multicast WiNET control traffic into account indeciding the GAP Countdown. FIG. 3 is an Example illustrating onedefinition of LAP Countdown, LAP Cycle, and GAP Countdown.

One embodiment of the LAP Information Element (“LAP IE”) format is shownin Table 2, where the LAP Status is set to “1” during the local accessperiod. The LAP Countdown can be dynamically set to the number ofsuperframes until the start of the next local access period. LAP Cycleis the number of superframes between the starts of two local accessperiods (See FIG. 3).

TABLE 2 LAP field format 2 bytes B15–b1 b0 LAP Cycle LAP Countdown LAPStatus

LAP IEs can be used to help source devices decide when theircorresponding receivers are active and ready to receive traffic. The LAPIE is preferably implemented to be heard by all neighbors and so LAP IEscan be transmitted during every global access period. In one embodiment,a device is configured to enter into the active mode at the start of itslocal access period. A device that enters the active mode can stay inthe active mode in the current superframe if the device has receivedtraffic in the previous superframe. On the other hand, a device canleave the active mode if the device has not received traffic in somenumber of previous superframe(s), some period, etc. This period can befixed, variable, depend on multiple factors, or only depend on traffic.For example, if at least mLAPtimeout (say 2) superframes have passedwithout receiving any WiNet traffic, the device may go into thehibernation mode. Source devices should send their traffic as early aspossible in their receivers' local access periods. The LAP Cycle fieldcan be changed only during the global access period. Thus, a sourcedevice that hears its receiver's LAP IE has enough information about itsreceiver active/hibernation modes for the entire duration between globalaccess periods. In one embodiment, the LAP Cycle dictates the frequencyof local access period and devices can recommend (through some controlcommand) a certain LAP Cycle to their corresponding receivers. Thiscycle should capture the source traffic characteristics.

As the above examples illustrate, in one embodiment to receive broadcasttraffic (i.e., ARP), network devices should be in the active mode. Theglobal active period (“GAP”) can be used in the above-describedembodiments as one mechanism for providing an interval during whichdevices (all devices in one embodiment) are set to be in the activemode.

To receive unicast traffic, a sender should know whether the destinationis active, or if not, when it will be active. Therefore, in oneembodiment devices are configured to announce when they will be active,i.e., their local active period to receive traffic. In the exampleenvironment, for example, WiNET sources can use their destinations'local access period to schedule unicast transmission.

As stated above, in one embodiment the bridge announces the globalaccess period in its beacon. If no bridge is present, the neighborhoodglobal access period can be defined as the first X superframes of thelocal access period of the device with the smallest beacon slot number.

It may be useful for devices to propagate the learned global accessperiod. Therefore, in one embodiment a device can be configured toannounce broadcast traffic in the global access period. It isinteresting to note that global access periods misalignment may resultin more active time. Although this may not break the scheme, it mayresult in less energy saving (due to the need for more than one globalaccess period).

As the above examples illustrate, there are numerous techniques forimplementing various embodiments of the present invention. FIG. 5 is aflowchart illustrating one example method in accordance with the systemsand methods described herein. The global access period can be defined ina step 500. During a global access period multiple devices can be in anactive mode. This can allow each device to be communicated with,assuming each device is in range, functioning correctly, powered on,etc.

The duration of the global access period can be based on traffic. Forexample, after not transmitting or receiving traffic for more than ysuperframes, the global access period can end. Further, the countdown tothe next global access period can be based on historical data related tobroadcast traffic.

The global access period can be created by a bridge device. The bridgedevice can announce the global access period in its beacon. Thus, anydevice that receives the bridge device beacon can determine the globalaccess period. In some cases devices can be out of range of the bridgeand thus, unable to receive the bridge device's beacon. If theout-of-range devices are within range of other devices in the networkthat are in range of the bridge then the learned global access periodcan be propagated from the bridge to the in-range device and from thein-range device to the out-of-range devices. In some cases it can takemultiple “hops” for an out-of-range device to learn the global accessperiod.

In one embodiment, if no bridge is present, the Neighborhood globalaccess period can be the first X superframes of the local access periodof the device with the smallest beacon slot cycle. It will beunderstood, however, that many other Neighborhood global access periodscan be defined depending on the particular implementation. For example,the Neighborhood global access period can be the first X superframes ofthe local access period of the device with the largest beacon slotcycle, the last X superframes of the local access period of the devicewith the smallest beacon slot cycle, etc.

In one embodiment any device can announce broadcast traffic in theglobal access period. For example, in a step 502 each destination devicecan announce its local access period. In one embodiment a destinationcan change its local access period every global access period. Byannouncing a local access period during a global access period it can bemore likely that a source device in a network will receive theinformation. This is because all devices should be active during theglobal access period and as indicated by a step 510 a source device cancheck for a recipient device's local access period, for example, duringthe global access period. By checking during a receiver device's knownglobal access period a source device can reduce the amount of time thatit spends in the idle state waiting for its destination to become activebecause, for example, the source can wake from hibernation at the sametime that the destination awakens from hibernation.

At some time, in a step 512, the source device can determine that it hastraffic for the recipient or receiver device. This determination cangenerally be at any time. For example, if the source determines that ithas traffic for the recipient device at the end of a local accessperiod, perhaps too late for transmission during that local accessperiod, the source device can wait until the next local access period.

During a step 504 a device can awaken, e.g., enter an active mode, forits local access period. During this time a source device can schedule atransmission, a step 514. Generally the transmission can be scheduledfor some time during the current local access period, however, in oneembodiment, transmissions can occur in subsequent local access periods.In a step 516 the source device can wake up, if it was asleep and in astep 518 the source device can transmit information to the device, e.g.,during the current local access periods. Thus, the device can receivethe data, a step 506 and then hibernate, a step 508.

In one embodiment a source can transmit its traffic early in areceiver's local access period so that, for example, so that thereceiver device can hibernate sooner after there is no data left to betransmitted. In this way power can be conserved because the local accessperiod can be shorter. In one embodiment a receiver device can stayactive (e.g., extend the local access period) as long as there is databuffered for transmission or reception.

In one embodiment, a source can recommend a certain LAP Cycle fordestination devices, for example, in cases where the data is to betransmitted in a subsequent local access period. The recommendation candepend on, for example, application latency, buffer space, etc.

FIG. 6 is a block diagram illustrating an example of global and localaccess periods. The diagram illustrates the global and local accessperiods for three devices, a bridge device, a device “A” and a device“B”. Time increases from left to right across the page. At 600 a globalaccess period for each device occurs. During the global access perioddevice A can transmit a local access period. For example, during theglobal access period 600 device A can transmit information indicatingthat it will have a local access period 602 at some later time.

The local access period can be fixed or variable. For example, it can beincreased if more data is expected to be received or decreased if lessdata is expected to be received. For example, after not transmitting orreceiving traffic for y superframes, the device can hibernate. The valueof y can be, for example, any integer number (e.g., 2). Thus, assumingthat the LAP period was p, the invention can be implemented such thatthe device is unnecessarily active for no more than y/p during eachlocal access period. In one embodiment the value of “y”, the number ofsuperframes not transmitting or receiving traffic, for the local accessperiod can be the same as the value of “y” for the global access period,as indicated by the use of the same variable, “y”. It will beunderstood, however, that in other embodiments that two waiting periodscan be different.

At some time indicated by 604 Device B can determine that it has trafficdestined to Device A. Because Device B knows when Device A's localaccess period occurs, it can wait to transmit the traffic until thestart of the local access period 602 as indicated by transmission 606.This transmission can be at the start of the global access period 602,In this way, the length of time of the local access period can belowered. At 608 the next global access period can occur. As discussedabove, the global access period can be variable, as indicated on thefigure.

FIG. 7 is a block diagram illustrating another example of global andlocal access periods. A first global access period 700 is shown. globalaccess periods 700 and 702 can occur periodically, for example, they canoccur based on a GAP countdown timer. The GAP countdown timer can varydepending on, for example, historical data on broadcast traffic.

During this global access period 700, device A can indicate when itslocal access periods 704 and 706 will occur. Similarly to the globalaccess periods 700 and 702, local access periods 704 and 706 can occurperiodically based on a LAP Countdown timer. The LAP countdown timer canvary depending on, for example, historical data on broadcast traffic. Inone embodiment, however, the LAP countdown timer only varies everyglobal access period 700 and 702 because this is when the local accessperiod info ration is transmitted to other devices. Thus, the cycle canbe fixed between global access periods.

FIG. 8 is a block diagram illustrating another example of global andlocal access periods. FIG. 8 is similar to FIG. 7. Specifically, theexample for the Bridge and Device A are the same. In the example of FIG.8 Device B has traffic for Device A. (Recall that this is similar toFIG. 7). In the example of FIG. 8 device B determines that it hastraffic for Device A at 800, after Device A's first local access period704 and after Device B's first local access period 802. Device B mayhave determined it has traffic for Device A because, for example, itreceived the traffic from another deice during it's local access period802. Device B can transmit it's traffic during local access period 706.Device B knows when Device A's local access periods will be because thelocal access periods can be transmitted during global access period 700.Additionally, the periodicity of the local access periods can betransmitted during the global access period. Thus, Device B candetermine when, for example, local access period 704 is going to occur(or when it occurred) and based on the periodicity, when local accessperiod 706 is going to occur (or when it occurred). Thus, when Device Bdetermines that it has traffic for Device A it can determine when itmight be able to transmit that traffic to device A based on when thenext local access period is scheduled to occur.

In one embodiment a network device can communicate with all of itsnetwork neighbors. A network device's neighbors can be, for example, anyother network devices that are operating under the same or similarnetworking standards such that communication between the devices ispossible and where the devices are in range of each other. Because manyof these types of devices can be portable, a device's neighbors canchange from time to time.

In one embodiment communication between neighbors can be delivered byunicasting multiple copies of the same traffic. An example of onedevice, device “D”, communicating with multiple devices, “A”, “B”, and“C” is shown in FIG. 9.

FIG. 9 is a block diagram illustrating another example of global andlocal access periods. As illustrated in FIG. 9 a broadcast trafficrequest 900 can be sent. In response to the broadcast request 900 device“D” can send messages 902, 904, and 906. These messages 902, 904, and906 can be sent during local access periods for devices “A”, “B”, and“C”, 908, 910, and 912 respectfully. For example, in one embodiment anIP can send an ARP request to WiNet.

It can, however, in some embodiments, be advantageous to send trafficone time, (multicasting) rather than unicasting multiple copies. Thiscan, for example, cut down on the amount of time a source needs to beactive.

In one embodiment a mechanism can be implemented to allow some level ofaccess period overlap to occur among devices. For example, in oneembodiment the relationship between global access periods and localaccess periods for different devices within a network can be defined bya set of mathematical equations such that two or more devices within aneighborhood in a given network have overlapping global access periods,local access periods, or both.

FIG. 10 is a block diagram illustrating an example of overlapping globalaccess periods in which Device “A” and Device “B” are in the sameneighborhood, in other words, they can “hear” each other, e.g., they arein range such that that they can send and receive transmissions to eachother. Device “B” and Device “C” are also in the same neighborhood,e.g., they are in range such that that can send and receivetransmissions to each other. Note that in this example, Device “A” and“C” cannot hear each other. They are out of range such that they cannotsend and receive transmissions to each other. At least not directly.They might be able to, however, send transmission to each other using,for example, Device “B” as an intermediary.

Each device in a network can announce a local access period. This can bethe time when a device is active and ready to exchange packets. Examplesillustrating local access periods relative to various global accessperiods are illustrated in FIGS. 6, 7, and 8. In one embodiment thetiming of one or more local access periods can be defined usingequations or other relationships such that one or more local accessperiods for two or more devices overlap.

For example, a LAP Cycle, the periods between two consecutive localaccess periods, can be defined using a periodic equation. One suchequation is:

LAP Cycle Period=Δ*2^(n)  (EQ1)

In the equation above n=0, 1, 2, . . . , N, where N and Δ can be fixed.For example, N and Δ can be numbers that are predetermined for a givennetwork, a given set of network devices, etc. In one embodiment thedevices can be configured to become active every Δ*2^(n) superframes.The frequency (n) can be determined based on, for example, incoming oroutgoing message traffic, power consumption needs, etc. Further, in oneembodiment, n can be determined individually for each particular device.

The resolution of a particular embodiment, Δ, can be an integer (e.g.,Δ=4). The resolution is the minimum number of superframes in a LAPcycle. Thus, for Δ=1 the minimum number of superframes in a LAP cycleis 1. (The LAP cycle is 1 when n=0.) For Δ=2 the minimum number ofsuperframes in a LAP cycle is 2. (The LAP cycle is 2 when n=0.) Etc.

N can be a fixed number that can be based on the communication standardfor a given set of devices in a network. For example, N can be set bythe MAC Standard maximum hibernation time (e.g., N=8).

Thus, LAP cycles can be indexed such that there can be a time periodwhen all neighbors of a device within a given network are active. Forexample, every device can advertise in its beacon (as part of WiNet ASIEfor example) its LAP Cycle, n, and an Active Cycle Start Time (“ACST”).The Active Cycle Start Time is the number of super frames until thedevice starts a new hibernation/active cycle. This can be similar toBeacon Period Start Time (“BPST”). A hibernation/active cycle can beΔ*2^(n) superframes.

When a device is turned on, powers up, etc. it can join a beaconinggroup in a certain channel. If the device joins a beaconing group in acertain channel, it can select the Active Cycle Start Time that isadvertised for that beaconing group. If the device does not receive anybeacon with an Active Cycle Start Time the device can select an ActiveCycle Start Time. Merging devices can adopt the Active Cycle Start Timeof the devices that they merge with. (similar to BPST).

Returning to FIG. 10, each device in a neighborhood, Devices A and B orDevices B and C, for example, can announce a global access period. Thiscan be the time when, for example, A, B, and C are active and ready toexchange packets. Similarly to local access periods, in one embodimentglobal access periods can be defined using equations. One such equationcan be derived from the local access periods equation. Recall that:

LAP Cycle Period=Δ*2^(n)  (EQ1)

If m is the maximum of all local access periods indexes of any neighbors(e.g., max(n_(i))) then the global access periods can be defined as:

GAP Periodicity=Δ*2^(m)  (EQ2)

In other words, the GAP Periodicity should be at least as long as themaximum LAP Cycle Period, otherwise some devices might never have alocal access period between global access periods because the globalaccess period would end first. In one embodiment the global accessperiod is the time when a device should send its broadcast/multicastcontrol traffic related to the active cycle start time. Further, theglobal access period can be defined based on the neighbors of eachdevice. Thus, various devices can have different global access periodsbased on the neighbors they “hear.” For example, one global accessperiod for one neighborhood, another global access period for anotherneighborhood.

Recall that, in FIG. 10, it was assumed that A and B can hear eachother, B and C can hear each other, but that A and C cannot hear eachother. Thus, A's neighborhood includes B, B's neighborhood includes bothA and C, and C's neighborhood includes B. In other words, even though Aand C are both in B's neighborhood, they are not in each other'sneighborhood. Thus, A's global access period can be based on B (and anyother devices it “hears”). C's global access period can also be based onB (and any other devices it “hears”). B's global access period, however,can be based on both A and C (and any other devices it “hears”). Thiswill be discussed in more detail below with respect to the specificexample of FIG. 10.

In one embodiment information related to a local access period can bestored in a LAP IE that is a 2 byte field. For example:

TABLE 3 LAP IE field format xxx (8 + log2Δ) bits b2–b0 reserved ACST n

Again, the local access period can be variable. For example, it can beincreased if more data is expected to be received or decreased if nomore data is expected to be received. For example, after nottransmitting or receiving traffic for y superframes, the device canhibernate. The device can examine the TIM IE when determining if itshould hibernate.

In one embodiment devices can negotiate LAP Indices. This can allow thedevices to determine the optimal activity period amounts themselves. Forexample, based on the amount of traffic. As discussed above, a sourcecan recommend a certain LAP cycle for destination devices that it hastraffic for, in other words, a source can recommend a value for n. Thevalue recommended can, for example, depend on application latencyrequirements, buffer space, power consumption, etc. In some embodimentsdevices can change their LAP cycle only during a global access periodwhen all or most of the other devices can hear the change.

In FIG. 10 assume that A and B can hear each other and that B and C canhear each other. Further assume that A and C cannot hear each other.Recall that the LAP Cycle Period is Δ*2^(n). For this example, assumethat Δ=4 superframes. Thus, Device A's a local access period 1000, 1002,1004, 1006, and 1008 will occur every 4 superframes. (For Device A n=0,thus 4*2⁰=4). Because, for Device B n=1, Device B's a local accessperiod 1010, 1012, and 1014 will occur every 8 superframes. (4*2¹=8).Because, for Device C n=2, Device C's a local access period 1016 and1018 will occur every 16 superframes. (4*2²=16).

The global access period can be defined at any point in which allrelevant devices in a given neighborhood are active. Typically, in oneembodiment, this might occur at the same time as the local access periodfor the device or devices with the longest LAP cycle time. Therefore, inone embodiment, the global access period occurs at the maximum LAP indexfor the set of relevant neighbors.

Referring to FIG. 11, an example method of determining a global accessperiod will now be discussed. In a step 1100 a device can determine itsrelevant neighbors. In one embodiment these can be any devices withinrange that are part of the same network, however, in another embodimentfewer than all devices within range and part of the same network may beconsidered to be relevant neighbors. In a step 1102 the device candetermine which neighbor or neighbors have the longest LAP Cycle Time.Thus, in one embodiment, the global access period can be set as themaximum LAP index for the set of relevant neighbors in a step 1106.

An example of determining global access periods that can use, forexample, the steps of FIG. 11 will now be discussed with respect to FIG.10. Thus Device A's global access periods 1020, 1022, and 1024 occursevery 8 superframes. This is because A and B can hear each other and Bhas the larger local access period index. Thus, for Device A tocommunicate with device B it can have a global access period thatcoincides with when Device B will be communicating, e.g., during the 1,8, 16, etc. superframe. Similarly Device B's global access period's 1026and 1028 occur every 16 superframes based on device C's larger localaccess period index.

It will be understood that while the example above illustrates sendingtraffic one time rather than unicasting multiple copies, in anotherembodiment, a combination of multicasting and unicasting or acombination of more than one multicast can be used in some embodiments.

As noted above, with many communication devices, active and hibernationmodes may be specified to allow devices to power down some or all oftheir functionality such as, for example, to conserve power. Forexample, according to the WiNet specification, a device periodicallygoes into active mode. The periodicity of going into active mode isreferred to as the local cycle. In one embodiment, a WiNet device canchoose the value of its local cycle according to the following formula:

Local cycle=2^(n) superframes,  (EQ3)

where n is the local cycle index, i.e., frequency;

0<=n<=wMaxLocalCycleIndex.

As noted above, in order to synchronize with neighbors' local cycles, adevice can be configured to maintain a global cycle start time for itsneighbors. A new global cycle can be started every2^(wMaxLocalCycleIndex) superframes. The device can set the global cyclestart countdown (“GCSC”) field in its WiNet Identification InformationElement to the number of superframes before the start of the next globalcycle, not including the current superframe. In one embodiment, theglobal cycle start countdown value is (2^(wMaxLocalCycleIndex)-1) in thefirst superframe of every global cycle and is decremented by 1 in everysubsequent superframe. A value of zero indicates a new global cycle willstart at the end of the current superframe.

If two devices that have different global cycle start times came intorange the two devices might need to align their global cycle starttimes. In order for the two devices to align there global cycle starttimes the devices might need to be in the active mode for longer thanthey would be if their global cycle start times are aligned. This canresult in a greater expenditure of energy. Thus, one embodiment of theinvention enables alignment of global cycle start times.

For example, in one embodiment the systems and methods described hereincan be applied to devices that implement the WiNet specification. TheWiNet specification does not provide a mechanism to synchronizedifferent global cycle start times. So if two devices that havedifferent global cycle start times came into range, the WiNet protocoldoes not specify how the two devices align their global cycle starttimes. Therefore, such devices might need to be in the active mode forlonger than they would be if their global cycle start times are aligned.This can result in a greater expenditure of energy. Thus, one embodimentof the invention enables alignment of global cycle start times.

According to one embodiment of the invention, a system and method toprovide alignment of hibernation and active cycles is provided. In oneembodiment, this can be used to better enable devices to awaken at thesame time, or temporally close to one another such that they can haveoverlapping (at least to some extent, if not entirely overlapping)active times. In terms of the example environment, in one embodiment, amechanism to enable devices to align their global cycle start times isprovided.

Referring now to FIG. 12, in one embodiment, when a device, D1, receivesa beacon in a step 1270 from one of its neighbors, D2, device D1 can beimplemented to get device D2's global cycle start countdown value in astep 1272 and to check it. In one embodiment, the check can be performedby comparing D2's global cycle start countdown value with its owncountdown value in a step 1274. If the beacon from D2 contains a globalcycle start countdown value that is different from the device's ownglobal cycle start countdown, the device D1 in this embodiment can beimplemented to check the following condition:

[GCSCself−GCSCneighbor]modulo256<128,  (EQ4)

Where, GCSCself is the global cycle start countdown of the device thatis checking the condition (D1 in this example), and GCSCneighbor is theglobal cycle start countdown of its neighbor (D2 in this example). Note,however, that in one embodiment both devices D1 and D2 can be configuredto check this condition from their own perspectives. One of ordinaryskill in the art would, after reading this description, understand howthis checking can be performed among more than two devices and how othermetrics can be chosen. Also note that in one embodiment the protocol canbe implemented using either “less than” or “greater than” in (EQ4), aslong as that choice is consistent for all devices.

For each device, if condition (EQ4) is satisfied, then the device setsits global cycle start countdown to match the global cycle startcountdown of the other device 1276. Otherwise, the device does notchange its global cycle start countdown. The above inequality translatesto the following: if a device's global cycle start time falls into thefirst half of a neighbor's global cycle, then the device changes its ownglobal cycle start time to the global cycle start time of that neighbor.Otherwise, the device does nothing.

Note that in one embodiment this condition (EQ4) is checked by bothdevices D1 and D2. In the example embodiment, however, the condition isdesigned such that it will become true for one or the other of the twodevices, to help ensure that there won't be any instability in the thisprotocol, for almost all cases. However, there can be a corner case inwhich both devices will be led to the same conclusion. With the givenmetrics, there is a probability of 1/256 that the two global cycle starttimes differ in exactly 128 superframes. This condition can be checkedin a step 1278. In this case, both the device and its neighbor would endup with the same conclusion when executing the condition of (EQ4).Therefore, in one embodiment a tie-breaker can be included.

For example, in such a case, i.e., when

[GCSCself−GCSCneighbor]modulo 256=128,  (EQ5)

each device can be configured in one embodiment to set its global cyclestart countdown for the next superframe to any random number between 0and 255, and continue normal operation steps (e.g., 1272, 1274, and 1276above). With a probability of (1-1/256), condition (EQ5) no longer holdstrue.

Including this embodiment, with the test of condition (EQ4), the totalproposed algorithm can be implement in one embodiment as the following:

1. At each superframe that a device is active, for each of itsneighbors, the device checks condition (EQ4), steps 1272 and 1274. Ifcondition (EQ4) is true, then the device shall set its global cyclestart countdown to match the global cycle start countdown of theneighbor, step 1230.

2. Otherwise, the device checks condition (EQ5), e.g., step 1274. Ifcondition (EQ5) is true, the device can:

-   -   a. Change GCSCself to a random value—for example, to a random        integer uniformly distributed over the range [0, 255], step        1280.    -   b. Stay active for the next superframe (go to step 1372).

3. Otherwise, do nothing, step 1282.

Note that in one embodiment, staying active for the next superframe (seestep 2b in the immediately above 3 steps) may not be specified in aprotocol as two devices that intend to communicate will naturally stayactive for the next superframe to conduct their network activities.

To further illustrate this technique, a few examples are now provided.In a first example, assume that devices A and B have just received eachothers' beacons, and that their global cycle start countdown values are250 and 240, respectively.

Device A computes the left hand side of (EQ4) and the result is 10, soit matches its global cycle start countdown to the one of B. Device Bcomputes the left hand side of (EQ4) and the result is 246, so it doesnothing. Thus, in this case, the two devices have converged to theglobal cycle start time of device B.

Assume that during this time, device C, which is a neighbor of A and soits global cycle start countdown is the same as the original globalcycle start countdown of device A, is hibernating. Assume that 245superframes later, device C goes into the active mode. Device C's globalcycle start countdown is now 5. Devices A and B's global cycle startcountdown is now 251. C computes the left hand side of (EQ4) and theresult is 246, so it must change its global cycle start countdown tomatch the one of B and A. Hence, in this example, all devices convergedto one global cycle start time.

A second example illustrates the so-called “corner case.” In thisexample, assume that devices A and B have just received each others'beacons, and that their global cycle start countdown values are 128 and0, respectively.

Device A and B compute the left hand side of (EQ4) and the result is128. So in accordance with the embodiment disclosed above, both devicespick a random number between 0 and 255. Assume, for example, that theypicked 10 and 40, respectively. Both devices announce their choices inthe next superframe.

Now, both devices again observe different global cycle start time.Particularly, using the example conditions above, device A computes theleft hand side of (EQ4) and the result is 226, so it does nothing.Device B computes the left hand side of (EQ4) and the result is 30, soit must match its global cycle start countdown to one of the A. Thus, inthis case, the two devices have converged to the global cycle start timeof device A.

The example immediately above illustrates a “corner case.” Devices A andB have just received each others' beacons and have global cycle startcountdown values of 128 and 0, respectively, at the beginning of theexample. This “corner case” example illustrates a scenario for aligningthe global cycle start times of two network devices. Thissynchronization can be applied to more than two devices in single-hopand multi-hop networks. Therefore, example embodiments for each scenarioare now described.

Referring now to FIG. 13, in one embodiment, when a device, D1, receivesbeacons 1300 from more than one of its neighbors, D2, D3, etc. it can beimplemented to check for device D2, D3, etc.'s global cycle startcountdown value in step 1310 and to compare the global cycle startcountdown values with its own 1320. (Similar to FIG. 12).

Consider the case of a single-hop network. In such a network, consideran example of a network device in communicative contact with a pluralityof other network devices, a step 1300. Let GCSC₁, GCSC₂, . . . ,GCSC_(K) be the global cycle start countdown values that are received bya first network device in a superframe and that are different from thatparticular device's global cycle start countdown. The device can get theGCSC for each of the K devices. For every k, where k=1, 2, . . . , K,the device shall (in step 1320):

1. Check the following condition:

[GCSC _(self) −GCSC _(k)]modulo 256<256/K,  (EQ6)

2. If condition (EQ6) is satisfied, then the device sets its globalcycle start countdown to match GCSC_(k). (Step 1330). Otherwise, thedevice does not change its global cycle start countdown.

In the above protocol, GCSC_(self) is the global cycle start countdownof the device that is checking the condition. This protocol can bestated another way: if a device's global cycle start time falls into thefirst 256/K superframes of a neighbor's global cycle, then the devicechanges its own global cycle start time to the global cycle start timeof that neighbor. Otherwise, the device does nothing. It should be notedthat this example protocol can be implemented with “less than” or“greater than” in the test of equation (EQ6), but that choice ispreferably consistent for all devices.

It should be noted that in some applications there may be a corner case,when the different global cycle start countdown values are exactly 256/Ksuperframes apart, a step 1340. In one embodiment, when this casearises, each device is to set its global cycle start countdown for thenext superframe to any random number between 0 and 255, step 1350 andcontinue normal operation: step 1 and 2 above. Otherwise the device canwait for the next beacon.

In cases where not all devices are in each others' ranges, the methodexplained above may not work. Referring back to FIG. 10, the followingexample illustrates a challenge that may arise with the above approachin a multi-hop network. Recall that A and C were neighbors, B and C wereneighbors, and A and C were not neighbors. For example, the threedevices, A, B, and C, can be in a line topology, A-B-C, where A and Bare in communication range with each other, B and C are in communicationrange with each other, but C and A are not in communication range witheach other. To illustrate the example, consider an example scenariowherein when these three devices hear each other for the first time, theglobal cycle start countdown value of A, B, and C are 0, 100, and 1,respectively. After each device applies the above two steps, none of thedevices would decide to change its global cycle start countdown.Therefore, the global cycle start countdown values in this network wouldnot be aligned.

Therefore, either one or a combination of the following enhancements orsteps 1380 can be added to the above two steps in order to aligndifferent global cycle start countdown values in multi-hop networks. Inone embodiment, a device applies the two steps explained above will bediscussed. (The device checks the condition of EQ6 and if the conditionis satisfied the device sets its global cycle start countdown to matchGCSC_(k).) But in addition, whenever the observed number of differentglobal cycle start countdowns, K, is higher than 2, a step 1360, thedevice is configured to apply one or more enhancements 1180. Referringnow to FIG. 14, one example enhancement 1180 will be discussed. Wheneverthe observed number of different global cycle start countdowns, K, ishigher than 2 (step 1360), in one embodiment, the device can checkagain. The check can occur after a number of superframes, step 1400. Inone embodiment the wait can be 3 superframes. If K is still the same ina step 1402 the device can apply the same steps but can replace K withK−1 in the Condition (EQ6) above in a step 1404. Otherwise, in a step1406, the device may not repeat the steps with K=K−1.

One advantage of using K−1 in the Condition of EQ6 is that after one ormore iterations, at least one device will match its global cycle startcountdown with one of its neighbors. Let us reconsider the line topologyexample A-B-C. In this case, B will use K=3 in Condition of EQ6. Butsince after say 3 superframes, K is still 3, device B will use K=2 inCondition of EQ6, and this will result in B changing its global cyclestart countdown to either A or C. So now the network of three deviceshas only two global cycle start countdowns, and global cycle startcountdown alignment can be simply accomplished using steps 1 and 2.(This can be part of Step 1380).

In another embodiment, a device that sees k different global cycle startcountdowns (where k>2 including itself, step 1360) in superframe n, itcan be configured to choose a random number (r) in a step 1500. In oneembodiment, r can be chosen to be between, for example, 1 and k, and thevalue for k can be chosen as, for example, the number of neighbors.

In a step 1502, at superframe n+r, the device tests Condition (EQ6) withthe value of K=2 and in the order of devices in which the global cyclestart countdowns were transmitted in that superframe. In a step 1504when it is superframe n+k, if k is still larger than 2 the process isrepeated in a step 1506. One advantage that might be achieved by thisapproach is that devices can be implemented to test Condition (EQ6) atdifferent times, thus improving the chances of aligning global cyclestart countdown values. (This can be part of Step 1380). If atsuperframe n+k k is not still greater than 2 then the steps may not berepeated, a step 1508.

In still another embodiment, a device that sees k different global cyclestart countdowns (where k>2 including itself) in superframe n, then withprobability 1/k, the device checks Condition (EQ6) assuming K=2.Preferably, this can be done in the order in which the global cyclestart countdowns were transmitted in that superframe. In one embodiment,if the condition is satisfied, the device changes its global cycle startcountdown to match its neighbor's global cycle start countdown withwhich the condition was satisfied. This process can be repeated untilall global cycle start times are aligned. (This can be part of Step1380). When K<=2 the method can continue at a step 1370, in other words,at least in some embodiments, the enhancements are not applied.

In accordance with another embodiment of the example environment andother communication environments, various hibernation protocols can beimplemented. For example, in accordance with one embodiment, a devicecan be assigned an anchor device status to facilitate networksynchronization or other network functions. After a device awakens, itcan be configured to go into hibernation mode once the negotiation isover and if it has determined that is it not an anchor device. However,in some cases, a neighboring anchor may disappear (move away or getturned off) after the negotiation is over (e.g., the mobile anchor walksaway). To address this challenge that is introduced by mobility, in oneembodiment, after the negotiation is over, if a device wishes to go intohibernation mode, it can be configured to first check that an anchordevice is still available. If not, then, in one embodiment the devicecan be required to stay in active mode to preserve power consumption.This can be implemented to occur every time the device wakes up and thenwants to return to hibernation.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for theinvention, which is done to aid in understanding the features andfunctionality that can be included in the invention. The invention isnot restricted to the illustrated example architectures orconfigurations, but the desired features can be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations can be implementedto implement the desired features of the present invention. Also, amultitude of different constituent module names other than thosedepicted herein can be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for theinvention, which is done to aid in understanding the features andfunctionality that can be included in the invention. The invention isnot restricted to the illustrated example architectures orconfigurations, but the desired features can be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations can be implementedto implement the desired features of the present invention. Also, amultitude of different constituent module names other than thosedepicted herein can be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

Although the invention is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead can beapplied, alone or in various combinations, to one or more of the otherembodiments of the invention, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more,” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise. Furthermore, although items, elements or components of theinvention may be described or claimed in the singular, the plural iscontemplated to be within the scope thereof unless limitation to thesingular is explicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedacross multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

1. A method of power management, comprising: defining a globalcommunication window, having a periodicity defined by a periodicrelationship; transmitting a local communication window, having aperiodicity defined by a periodic relationship to other devices in anetwork; waking from a hibernation state at a predetermined time for thelocal communication window; receiving a transmission from another devicein the network during the local communication window; and returning tothe hibernation state after the local communication window.
 2. Themethod of claim 1, wherein the relationships defining the periodicity ofthe global and the local communication windows are equations.
 3. Themethod of claim 2, wherein the equation defining the globalcommunication window is Δ*2^(m).
 4. The method of claim 2, wherein theequation defining the local communication window is Δ*2^(n).
 5. Themethod of claim 4, wherein n is determined, at least in part, based onmessage traffic.
 6. The method of claim 4, wherein n is determined, atleast in part, based on power consumption needs.
 7. The method of claim4, wherein n is determined, at least in part, based on a devicesavailable battery life.
 8. The method of claim 2, wherein the equationdefining the global communication window is Δ*2^(m) and the equationdefining the local communication window is Δ*2^(n).
 9. The method ofclaim 8, wherein n is equal to the largest value of n for a givenneighborhood.
 10. The method of claim 1, further comprising selecting anActive Cycle Start Time that is advertised for a particular beaconinggroup.
 11. The method of claim 10, further comprising a device selectingan Active Cycle Start Time if no beacon is received.
 12. A networkdevice comprising: a memory, the memory configured to storeinstructions; a processor coupled to the memory and configured toexecute the instructions to perform the following steps: defining aglobal communication window, having a periodicity defined by a periodicrelationship; transmitting a local communication window, having aperiodicity defined by a periodic relationship to other devices in anetwork; waking from a hibernation state at a predetermined time for thelocal communication window; receiving a transmission from another devicein the network during the local communication window; and returning tothe hibernation state after the local communication window.
 13. Themethod of claim 12, wherein the relationships defining the periodicityof the global and the local communication windows are equations.
 14. Themethod of claim 13, wherein the equation defining the globalcommunication window is Δ*2^(m).
 15. The method of claim 13, wherein theequation defining the local communication window is Δ*2^(n).
 16. Themethod of claim 15, wherein n is determined, at least in part, based onmessage traffic.
 17. The method of claim 15, wherein n is determined, atleast in part, based on power consumption needs.
 18. The method of claim15, wherein n is determined, at least in part, based on a devicesavailable battery life.
 19. The method of claim 13, wherein the equationdefining the global communication window is Δ*2^(m) and the equationdefining the local communication window is Δ*2^(n).
 20. The method ofclaim 19, wherein n is equal to the largest value of n for a givenneighborhood.
 21. The method of claim 12, further comprising selectingan Active Cycle Start Time that is advertised for a particular beaconinggroup.
 22. The method of claim 21, further comprising a device selectingan Active Cycle Start Time if no beacon is received.